It’s basically like having an underseat helmet compartment except it folds up and fits, er, under your seat. With a removable shoulder strap, it also serves very well for carting your helmet around.

What’s not? Only that chaining your helmet to a wheel while simultaneously zipping it into a bag is as fiddly as it sounds. And while the material is waterproof, the zip at the base isn’t, so if it really belts it down there’s chance your helmet will get damp.